Control system for fluid fuel burners



June 3, 1969 w. F. POTTS L CONTRQL SYSTEM FOR FLUID FUEL BURNERS Sheet of 5 Filed Sept. 29, 1966 Fr ll nvvc/vroxs."

WILLIAM F POTTS FRANCOIS DUVAL June 3, 1969 W. F. POTTS ET AL CONTROL SYSTEM FOR FLUID FUEL BURNERS Filed Sept 29, 1966 June 3, 1969 w. F. POTTS L CONTROL SYSTEM FOR FLUID FUEL BURNERS Sheet Filed Sept. 29,

2. :mEZ 59.6w uEd U w UN SE 85:? 0 005 DOV June 3, 1969 w. F. POTTs ET AL 3,447,880

CONTROL SYSTEM FOR FLUID FUEL BURNERS Filed Sept. 29, 1966 Sheet 4 Spark Defec or June 3, 1969 w. F. POTTS ET AL CONTROL SYSTEM FOR FLUID FUEL BURNERS Sheet 5 0 Filed Sept. 29, 1966 United States Patent Office Patented June 3, 1969 US. Cl. 431-27 25 Claims ABSTRACT OF THE DISCLOSURE Burner ignition and control system with pilot and main burner, and electrical valves, a blower, spark ignition, a flame sensor for both burners, a switch for sensing blower operation, a spark voltage sensor, a thermostat to complete a circuit to the blower, and to partially complete a circuit through the switch for ignition, a time delay device to complete the ignition circuit after a predetermined period to provide a prepurging of the burners prior to attempting ignition, a circuit for controlling the pilot valve adapted to be closed by the sparkvoltage sensorindicating sufficient spark voltage, and opened in response to the flame sensor indicating absence of flame, and a second time delay for preventing the actuation of the sensor for a predetermined interval after opening the pilot valve, the flame sensor actuating the main valve upon indication of flame at the pilot burner, and closing the pilot valve and deenergizing the ignition, the flame sensor closing the valve of the main burner upon absence of flame, a latching circuit and a manual reset to disable the ignition and the valve operation until manual actuation of the reset switch.

. This invention relates to control systems for safe operation of fluid fuel burners, the burnersbeing ignited by, a spark discharge and the .controlmeans being combinations of semiconductor devices. it i A burner system may comprise all or some of the following major units: A pilot or first burner,1a main or-second burner, fuel control valves for each burner, blower and blower motor for draft air, ignition means and control means. For the safe and successful operation of any system, a particularsequence of events is required depending on the complexity of the system; The principal. object of the invention, accordingly, i to provide a fluid fuel burner control system. with fuel ignition means and an automatic sequential program means for controlling the turning on and shutting off of fuel to the burners and ignition thereof for safe operation.

Another object is to provide a modular control system that: satisfies the requirementsfor any fluid fuel burner system with a minimum of complexity.

A further object is to provide a system which is lower in cost and smaller in size and more easily installed than presently existing control and ignition systems.

A'still further object is to provide a control system without moving arm contacts, heating-timing devices and electro-mechanical devices;

Stillanotherobject is to provide asystem which is modular in nature and in which combinations of readily available electronic components may be added or de- "leted for changing the functioning of the controls according to the complexity of the burner system with which thecontrols are to beused. I

Other objects and advantages will become apparent from the following description in conjunction with the accompanying drawings, in which: I 7

FIGURE l'is a diagrammatic view of a single burner system'and a, simple form of circuit for controlling the operation thereof;

FIGURE 2 is a similar view showing a control system with electronic components added to provide for a prepurge period;

FIGURE 3 is a similar view showing a control system with other components added to provide for a lockout circuit and a safety timing period;

FIGURE 4 is a similar view showing a control system with 'a flame sensing device and other components added to provide for continuous proof of flame, spark generator control, proof of ignition, actuating the fuel valve and lockout;

FIGURE 5 is a similar view showing a control system with other components added to provide for means to detect a partial short at the igniter electrodes; and

FIGURE 6 is a similar view showing a two burner system and a system of controls therefor further providing for a postpurge period.

Referring to FIGURE 1, a single burner 10 is provided with a solenoid operated fuel supply valve 11, the solenoid being shown at 12. Located in proximity to the burner are the igniter electrodes 13, 14, the latter being grounded.

A blower motor 15, for providing draft in the combustion chamber in which burner 10 is located, has a centrifugally operated switch 16 which closes when the motor reaches its normal operating speed to connect a common DC supply line 17 to its source of current.

A source of alternating current is represented by the terminals L and L across which the primary winding of a transformer 20 is connected. l is connected to a common return or ground line 21 and the secondary winding of transformer 20 is connected between the ground line and a reference point 22 to provide a secondary voltage of 24 volts RMS.

A thermostatically operated switch 23, located wherever necessary to call for heat from the burner 10, is connected to reference point 22 through the cathode and anode, in that order, of a diode 25, the junction 26 of one terminal of switch 23 and the cathode of diode being connected by a capacitor 27 to reference point 28 on line 21. Diode 25 and charging capacitor 27 rectify the voltage from transformer 20 to' approximately 30 volts DC available at reference point 26.

The other terminal of switch 23 is connected through resistor 30 to the gate terminal of a triac 31 and the junction of switch 23 and resistor 30 is connected through ,switch 16 to the common DC line 17 leading to the rest of the control circuitry.

Terminal L is also connected through the anode 1- anode 2 section of another triac 32 to a first input terminal 33 of a spark discharge voltage generator, components 35, 38-44, and one terminal of the winding of a secondary transformer 35 which is included in the voltage generator further described in the copending application Ser. No. 531,906 of William F. Potts, filed March 4, 1966 and issued May 9, 1967, as Patent Number 3,318,358.

The anode 2 terminal of triac 32 which is connected to transformer 35 is also connected through fuse 36 and motor 15 to line 21. The gate terminal of triac 32 is connected through resistor 37 to the anode 2 terminal of triac 31, the anode 1 terminal being connected to line 21.

The other terminal of the primary winding of transformer 35 is connected to one plate of a capacitor 38 the other plate being connected through a series combination of the anode-cathode of an SCR (silicon con, trolled rectifier) 40 and the anode-cathode of a diode 41, in that order, to the first terminal of transformer 35. The gate terminal of SCR 40 is also connected to this first terminal. The junction of the anode of SCR 40 and capacitor 38 is connected through a series combination of the cathode-anode of a diode 42 and a resistor 43 to line 21,

and the junction of SCR 40 and diode 41 is also connected through resistor 44 to line 21.

The sparking electrodes 13 and 14 are each connected to a respective secondary winding terminal of transformer 35 and the grounded electrode 14 is connected to line 21 and also, through a series combination of the anode-cathode of diode 45 and resistor 46, in that order, to electrode 13. r

The junction of diode 45 and resistor 46 is connected at reference point 47 to the base of a transistor 48 which, with components 45, 46, and 4855 forms a section of the circuit called the spark detector. Transistor 48 is an NPN transistor as are all the transistors hereinafter described unless otherwise noted. The point 45 is also connected to one plate of a capacitor 49, the other plate being connected to the common return line 21.

The collector of transistor 48 is connected through a resistor 50 to the common DC line 17 and the emitter is connected to line 21. The collector of transistor 48 is also connected to the base of another transistor 51 whose collector is connected through a resistor 52 to line 17 and through another resistor 53 to line 21. The emitter of transistor 51 is connected to line 21 and its collector is also connected to the gate terminal of an SCR 55.

The cathode of SCR 55 is connected to line 21 and its anode is connected to one terminal of the fuel valve solenoid 12 and to one plate of a capacitor 56. The other terminal of solenoid 12 is connected to the other plate of capacitor 56 and to reference point 22.

The operation of the circuit of FIGURE 1 starts with the closing of the thermostatically operated switch 23 calling for heat.

When switch 23 closes, positive DC voltage is applied through resistor to the gate-anode 1 section of triac 31, thus turning on triac 31. Alternating current is thus allowed to flow in the series circuit comprising line terrninal L the anode-gate section of triac 32, resistor 37, the anode 2-anode 1 section of triac 31, and line terminal L thus turning on triac 32. Line voltage is thus applied to the spark generator from triac 32 and, through fuse 36, to motor 15.

When the motor reaches normal speed the centrifugally operated switch 16 closes and applies positive direct current voltage to the common positive DC line 17.

When triac 32 is turned on, line voltage is also applied therethrough to the spark producing module, consisting of components 35 and 38-44, and electrodes 13 and 14, whose operation has been described in said copending application Ser. No. 531,906. A spark is produced between electrodes 13 and 14 when the supply line connected to terminal L is positive with respect to the terminal L line.

Spark detector circuit The spark detecting or sensing module consists of the voltage detector components 45, 46 and amplier components 48 through 55. Electrode 14 is grounded and this is a reference point for the spark detector circuit. The voltage at electrode 13 is led through limiting resistor 46 to the base of transistor 48 at reference point 47.

Diode is furnished to clip all negative going voltages and capacitor 49 tends to act as a filter condenser so individual voltage excursions will not alternately turn on and cut off transistor 48. When a voltage appears between electrodes 13 and 14 it is led as a pulse to the base of transistor 48 and changes the transistor from cut-01f to saturation for the period of the pulse.

Transistor 51, whose base is connected through resistor 50 to line 17, is saturated when transistor 48 is cut off and line 17 is grounded through resistor 52 and the collector emitter circuit of transistor 51. When transistor 48 becomes saturated, however, its collector-emitter circuit conducts, cutting off transistor 51, and the gate of the switch device, SCR 55, draws current through resistor 52 allowing current to flow in its anode cathode portion and allowing solenoid 12 to draw current from reference point 22, thereby turning on valve 11. When SCR 55 conducts it draws current every half cycle when reference point 22 is positive with respect to reference point 28 through the solenoid 12, at the same time charging capacitor 56'. When point 22 goes negative SCR 55 ceases to conduct and capacitor 56 discharges through solenoid 12 thus keeping the latter energized during the half cycle that SCR 55 is not conducting.

Capacitor 49 serves as a filter capacitor to discharge through transistor 48 to keep the pulse voltage at point 47 while the voltage is building up at capacitor 56.

On negative half cycles of the spark discharge voltage diode 45 conducts to prevent the base of transistor 48 from being damaged by high negative-voltages.

Each time spark discharge voltage appears between electrodes 13 and 14 the collector of transistor 51 rises from less than 0.2 volt positive potential to several volts positive. If there is no spark discharge voltage at electrodes 13 and 14, when they have been shorted, for example, transistor 48 is cut oif and transistor 51 is satu-- rated with a collector-emitter voltage of less than 0.2 volt.

When sparking occurs the spark detector provides a positive going signal at each spark discharge. This signal may be used to operate any suitable switching or relay 1 device which is sensitive to a positive voltage signal. In 1 this embodiment the positive signal is fed to the gate of the SCR which, when turned on, energizes solenoid 12 and opens fuel valve 11, allowing fuel to flow to burner 10 where it is ignited by the sparks at electrodes 13 and 14.

Resistor 53 operates as a clamping device from the gate to the cathode of SCR 55 to maintain the voltage at the gate below a predetermined limit.

So long as switch 23 remains closed, sparks are induced at the electrodes and fuel valve 11 is maintained open.

reason at electrodes 13 and 14 the valve 11 closes and burner 10 is turned off.

When switch 23 opens current is cut otf from motor 15 and the system returns to rest but in condition to recycle when switch 23 again closes and calls for heat.

Referring to FIGURE 2, means are provided to allow the motor 10 to run for a short period of time, referred to as the prepurge period, before spark discharges may occur and the fuel valve can open, so as to purge the combustion chamber of accumulated gases. The same burner 10 with associated electrodes 13 and 14 and supply valve 11 is shown in FIGURE 1. The same means for connectingline current to the motor and spark producing module and for applying DC voltage to line 17 is shown and the spark sensing section of the circuit, comprising components 48-52, is the same.

Switch In FIGURE 2, however, resistor 44 is connected, not directly, but through the anode-cathode section, in that order, of an SCR 58 to line 21, the gate terminal of SCR 58 also being connected through a resistor 59 to line 21.

Prepurge timer The gate of SCR 58 is also connected to the collector of a transistor 60 comprising, with components 61-66, the prepurge timing portion of the circuit. The collector of transistor 60 is also connected through resistor 61 to the common DC line 17 and the emitter of this transistor is connected to the common return line 21. The base of transistor 60 is connected to the collector of a transistor 62 and, through resistor 63 to line 17. The emitter of transistor 62 is connected to line 21 and the base is connected to the anode of a Zener diode 64 and through the Zener to the junction of .a series combination of resistor 65 and capacitor 66, the resistor 65 being connected to line 17 and capacitor 66 to line 21. I

In operation when motor 15 reaches its normal running speed, 24 volts is applied to line 17 through switches 23 and 16, as previously described.

As voltage is applied to line 17, capacitor 66 charges through resistor 65 and, when the charge equals the Zener voltage of Zener diode 64, the Zener conducts and current flows through the, base of transistor 62 which saturates. When the transistor saturates, current through resistor 63 to the base of transistor 60 is bypassed and transistor 60 is cut off. The collector voltage of transistor 60 thereupon rises from less than 0.2 volt positive to several volts positive. The time taken to charge capacitor 66 from zero to the Zener voltage of Zener 64 is die prepurge period.

The spark discharge voltage generator comprising components 35 and 38-43 is prevented from functioning during the prepurge period by SCR 58 since its gate is connected to the collector of transistor 60 which is at less than 0.2 volt positive potential during the pre-purge period. At the end of this period, when transistor 60 cuts off, the gate of SCR 58 draws current from line 17 through resistor 61. When the gate draws current, the anodecathode section of SCR 58 becomes conductive and allows the spark discharge voltage generator to function as briefly described in connection with FIGURE 1.

Resistor 59 from the gate of SCR 58 to its cathode is a clamping device to insure that the voltage at the gate does not exceed a certain maximum value.

As described above, fuel valve 11 will not open until sparks appear at electrodes 13 and 14 and are sensed by the spark detector circuit comprising components 45-55. It will also be apparent that when switch 23 opens again current to the motor 15 and spark generator 35, 38-43, will be cut ofi? and the system will return to rest and ready for another cycle.

Referring to FIGURE 3, the circuit there shown is essentially that shown in FIGURE 2 with further provision for shutting off and looking out the system should the burner fail to ignite or if the flame is extinguished for any reason but by the opening of switch 23. Provision is also made for a safety timing period in which, if the spark sensor does not indicate sparks occurring for a predetermined period, the system will go on lockout at the end of the safety period.

The same single burner and associated electrodes 13 and 14 and fuel supply valve 11 are used as shown in FIGURE 1 and the means for bringing line current to motor and spark module 35, 38-44, and for supplying DC current to the line 17 are the same as described above.

The spark detector, components 45-55, described in connection with FIGURE 1 and shown-in FIGURE 2, is the same as is the prepurge timer, components 60-66, described above and shown in FIGURE 2.

Safety timer The collector of transistor 60 in the prepurge timer is also connected tothe cathode of a diode 68 whose anode is connected to the cathode of a Zener diode 69 and to one plate of a capacitor 70. The cathode of this Zener is also connected to the junction of one terminal of a resistor 71 and the anode of a diode 72 whose cathode is connected to the collector of transistor 48 in the spark detector circuit. The other terminal of resistor 71 is connected to line 17 and the other plate of capacitor 70 is connected to line 21.

Lockout means The anode of Zener 69 is connected to the collector of a PNP transistor 73 and to the base of an NPN transistor 74. Transistor 74 has its emitter connected to line 21 and its collector connected to the base of transistor 73 and,

through a resistor 75, to a line 76 connected to reference point 26. The emitter of transistor 73 is also connected, through a resistor 77, to line 76.

Reset switch junction of capacitor 66, Zener 64, and resistor in the prepurge timer. Switches 78 and 79 are mechanically connected to operate in unison and are manually closable.

In operation, the safety timer begins to operate when the prepurge period ends with the saturating of transistor 60. During the prepurge period capacitor is prevented from charging through resistor 71 from line 17 by the series connection through diode 68 and through the saturated transistor 60 whose emitter is connected to the return line 21. Zener diode 69 will therefore not conduct and transistors 73 and 74 will remain cut off.

When the prepurge period ends and transistor 60 cuts off, as described above, diode 68 becomes reverse biased and capacitor 70 starts charging through resistor 71.

If spark discharges are not occurring at electrodes 13 and 14, transistor 48 in the spark detector will remain cut off and diode 72 will remain reverse biased and capacitor 70 will continue charging until its charge equals the Zener voltage or Zener diode 69. When this occurs Zener 69 conducts bringing current to the base of transistor 74 causing it to saturate.

When transistor 74 saturates there is a voltage drop across resistor and current flows to the base of PNP transistor 73 causing the latter transistor to saturate. With the saturation of transistor 73, the base of transistor 74 draws current from reference point 26 through line 76, resistor 77 and transistor 73. When this occurs both transistors are latched or locked on and in saturation.

Since the junction of resistors 75 and 77 is connected to reference point 26 and the cathode of diode rectifier 25 which is positive at all times, the lockout is independent of the operation of either switch 23 or switch 16. The lockout may only be unlocked by bringing the base of transistor 74 to zero.

Since the gate of triac 31 is connected to the collector of transistor 74, when transistor 74 saturates with a collector voltage of less than 0.2 volt, triac 31 will also cut off thus cutting oflf triac 32 and cutting off line voltage to motor 15 and the spark voltage generator. When the motor slows, switch 16 opens and DC current is cut off except to the lockout circuit.

When the cause of the lockout has been remedied the lockout maybe broken and reset by closing switch 78. Since the base of transistor 74 is connected by closing of switch 78 to the common return line 21, the transistor is brought to zero and the transistor cuts off. When transistor 74 cuts off the flow of current to the base of transistor 73 is cut off thereby cutting off the latter.

When switch 78 closes, switch 79 also closes and capacitor 66 in the prepurge timer is shorted preventing any accidental flow of current through Zener 64 and consequently any accidental starting of the motor 15 or the spark generator.

After switch 78-79 has been closed and thereafter opened, therefore, the system is efiectively reset for further operation acording to the call of the thermostatic switch 23.

Referring to FIGURE 4, another modification of the circuit shown in FIGURE 2 is there shown in which provision is made for a proof of i nition timing circuit (components 92-96), a modified lockout circuit (components 73-77, -118) and reset means therefor (components 78-80, a flame sensor (component 81) and an amplifier therefor (components 108-113), a modified fuel valve actuating circuit (components 103-107), a spark pulse integrator (com-ponents 98-102).

The same single burner 10 and associated electrodes 13 and 14 and fuel valve 11 are used as shown in FIG- URES 1 and 2 and the same means for bringing line current to motor 15 and the spark generator 35, 38-44 and for supplying DC current to the line 17.

The same prepurge timer 60-66 described above and shown in FIGURE 2 is used. The spark detector components 48-52 shown in FIGURE 4 are reversed from left 7 to right from their positions shown in FIGURE 2 but inspection will show that their arrangement is the same.

The flame sensor 81, disposed adjacent burner 10 may be either:

(a) A heat operated resistance device having a relatively high resistance when cold and a relatively low resistance when hot as, for example, a negative temperature coeflicient resistor or a temperature sensitive switch;

(b) A light sensitive resistance device which has a high resistance when not illuminated by light from the burner and a relatively low resistance when illuminated as, for example, a cadmium sulphide photo cell.

High resistance, as here used, is greater than about 150,000 ohms and relatively low resistance is less than about 5,000 ohms.

The flame sensor 81, in FIGURE 4, is connected in series across the terminals 82 and 83 as indicated by broken lines in the drawing.

Spark generator control The gate of SCR 58 in the spark generator is connected to the collector of a transistor 85, the collector being also connected by resistance 86 to 'line 17, and the emitter of transistor 85 being connected to the common return line.

The base of transistor 85 is connected to the collector of a transistor 87 and by a resistor 88 to line 17 so that transistor 85 is initially saturated preventing voltage from being applied to the gate of SCR 58.

The emitter of transistor 87 is connected to line 21 and its base is connected to the anode of a diode 90 and also through a resistor 91 to the collector of transistor 60 in the prepurge timer so that transistor 87 is not turned on until transistor 60 cuts oil? at the end of the prepurge period.

Proof of ignition timer The collector of transistor 60 in the prepurge timer is also connected, through a resistor 92, to one plate of a capacitor 93, the other plate of which is connected to line 21. The junction of resistor 92 and capacitor 93 is connected to the cathode of a Zener diode 94, the anode of which is connected to the base of a transistor 95.

The transistor 95 has its emitter connected to line 21 and its collector connected to the cathode of diode 90 in the spark generator control and to the lockout and fuel valve actuator circuits as hereinafter described. The collector of transistor '95 is also connected to the DC 'line 17 through a resistor 96.

Spark pulse integrator The collector of transistor 95 in the proof of ignition timer is connected through a resistor 103 to the base of a transistor 104 which base is also connected to the collector of transistor 101 in the spark pulse integrator.

Transistor 104 has its emitter connected to line 21 and its collector connected to line 17 and to the gate of SCR 55 through resistors 105 and 106 respectively. SCR 55 has its anode connected to solenoid 12, as described above in connection with FIGURE 1, and its cathode connected to line 21. The gate of SCR 55 is also connected through a resistor 107 to the flame sensor amplifier as hereinafter described.

Flame sensor amplifier The flame sensor 81 has one terminal 82 connected by a resistor 108 to DC line 17 and its other terminal 83 is connected to the base of a transistor 109 and, through a resistor 110, to line 21.

Transistor 109 has its emitter connected to line 21 and its collector connected to the base of a transistor 111, the cathode of a diode 112, and, through resistor 113, to line 17. The anode of diode 112 is connected to the lockout and reset switch as will be described.

Transistor 111 has its emitter connected to line 21 and its collector connected to line 17 and the gate of SCR 55 through resistors 114 and 107 respectively.

Lockout The junction between resistor 91 in the spark generator control and resistor 92 in the proof of ignition timer, which is at the collector of transistor 60 in the prepurge timer, is connected to the anode of a diode 115 whose cathode is connected to the cathode of a diode 116 whose anode is connected to the gate of triac 31.

The junction of the cathodes of diodes 11-6 and 115 is connected to the base of a PNP transistor 73, the collector of NPN transistor 74, and, through a resistor 75, to reference point 26 at the cathode of diode 25. Transistor 74 has its emitter connected to line 21 and its base connected to the collector of transistor 73 and to the anode of diode 112 in the flame sensor amplifier. The emitter of transistor 73 is connected through resistor 77 to reference point 26 as described in connection with FIGURE 3.

The base of transistor 74 is also connected as hereinafter described to the reset and to the collector of a transistor 117 whose base is connected to the collector of transistor 95 in the proof of ignition timer. The collector of transistor 117 is connected through resistor 118 to line 17 and the emitter of transistor 117 is connected to line 21.

Reset The junction of resistor 65, capacitor 66 and Zener 64 in the prepurge timer is connected through the anode and cathode of a diode 119 and a resistor 80, in that order, to one contact of a normally open reset switch 79 which is also connected through the cathode and anode, in that order, of a diode 120 to the anode of diode 112 in the flame sensor amplifier and to the base of transistor 74 in the lockout.

Switch 79 is normally open and is linked with another normally open switch 78 which may be manually closed to connect the gate of triac 31 to line 21.

The operation of the controls shown in FIGURE 4 is initiated by the closing of switch 23 to call for heat. Triacs 31 and 32 operate as described in connection with FIGURE 1 to supply line current to motor 15 and the spark generator and switch 16 closes when the motor comes up to speed.

The prepurge timer, components 60455, operates as described in connection with FIGURE 2, to prevent the gate of SCR 58 from turning on line current to the spark generator until transistor 60 is cut off.

At the end of the prepurge period, the spark generator control, components 85-91, allow the spark discharge voltage generator to function and spark discharges occur at electrodes 13 and 14.

Transistor 85 is initially saturated when switch 16 closes, its base being connected through resistor 88- to line 17. When transistor 60 cut oil, however, the base of transistor 87 draws current through resistors 61 and 91 and transistor 87 saturates cutting otf transistor 85. The gate of SCR 58 thereafter draws current through resistor 86 and SCR 58 becomes conductive turning on the spark generator.

Also, at the end of the prepurge period when transistor 60 cuts off, the proof of ignition timer components 92-96 begins to function.

Capacitor 93 begins to charge through resistors 61 and 92 until the voltage builds to the breakdown of Zener 94, the time interval being the proof of ignition period. Zener 94 then conducts and transistor 95 changes from cut off to saturation, the collector of transistor 95 dropping to a potential of less than 0.2 volt.

When transistor 95 saturates, transistor 87 cuts off because its base current is bypassed through the series combination of the collector-emitter of transistor 95 to line 21. With transistor 87 cut olf,, transistor 85 saturates, with its base drawing current through resistor 88, and SCR 58 cuts off since the source of current for its gate is bypassed through resistor 86, the collector-emitter of transistor 85 to line 21. As SCR 58 cuts off, of course, the further occurrence of sparks at the electrodes is halted.

When spark discharges are stopped transistor 101 cuts 01f and the base of transistor 104 draws current from line 17 through resistor 102 causing transistor 104 to saturate. Current through resistors 105 and'106 to the gate of SCR 55 is cut off, being bypassed through resistor 105, the collector-emitter of transistor'104, to line 21. SCR 55 is thus left wholly dependent on the flame sensor circuit to hold the gas valve open.

' 'When sparks occur at electrodes 13 and 14, before the end of the proof of ignition period, a positive pulse for each spark occurs at the collector of transistor 51 in the spark detector as described in connection with FIG- URE l. The pulses are integrated or stretched to provide a steady DC signal by the pulse integrator, components 98-102. Each positive pulse will charge capacitor 99 through diode 98 and resistor 52. Since these pulses are of short duration, about 200 microseconds, and since the pulses occur every 16,700 microseconds (at line voltage frequency 60 Hertz) capacitor 99 and resistor 100 must have a sufliciently long time constant so that the base of transistor 101 can draw current from the discharge of capacitor 99 for at least about three times the pulse period, 50,000 microseconds.

The steady DC signal actuates the fuel valve actuator, components 103-107. When transistor 101 saturates as a result of spark discharges occurring, transistor 104 will be cut off allowing the gate of SCR 55 to draw current from line 17 through resistors 105 and 106. This makes SCR 55 conductive and solenoid 12 is energized opening fuel supply valve 11 releasing fuel at burner where it is ignited by the spark discharges. This normally occurs well in advance of the end of the proof of ignition period.

Flame sensor 81, in the absence of flame at burner 10, has a high resistance and the voltage drop across resistor 110 will be very low, less than 0.2 volt, and transistor 109 will be cut off and transistor 111 is saturated and drawing current through resistor 114.

When flame is present at the burner, sensor 81 has a low resistance and the base of transistor 109 draws sufficient current from line 17 through resistor 108 and the sensor causing transistor 109 to saturate cutting off transistor 111 and allowing the gate of SCR 55 to draw current through resistors 1-14 and .107.

I Thus, during the proof of ignition period, the fuel valve is opened first by the proven occurrence of spark discharges and then is held open by the proven presence of flame at the burner.

If spark discharges are not proven by the spark detector by the end of the proof of ignition period, however, the lockout circuit, components 73 77,.115-118, operates to shut the system off and keep it locked-out until the system is manually reset. Also, if at any time, after the burner has been burning after the proof of ignition period, the burner goes out for any reason, the flame detector detects the absence of flame unless caused by the opening'of switch 23, the system will shut otf and go on lockout.

If flame sensor 81 has failed to detect flame when transistors 95 and 104 saturate, with transistor 111 also being in saturation, SCR 55 will cut off and close the fuel valve 11 since the gate of SCR 55 cannot draw current when transistors 104 and 111 are both in saturation. Further, in the absence of flame transistor 109 is cut off and diode 112 is reverse biased so that when proof of ignition period ends and transistor 95 saturates, it causes transistor 117 to cut off since the source of current to the base of transistor 117 through resistor 96 is bypassed through the collector-emitter of transistor 95. Y

The base of transistor 74 is able to draw current from line 17 through resistor 118 and transistor 74 saturates. PNP transistor 73 also saturates and the two transistors drawing current through resistors and 77 from reference point 26 keep each other in saturation, as described in connection with FIGURE 3.

At any time after the proofv of ignition period if flame sensor 81 fails to detect flame at burner 10 diode '112 becomes reverse biased, transistor is saturated because the proof of ignition period is over, and transistor .117 cuts off and lockout will occur.

The mutual saturation of transistors 74 and 73 locks out the rest of the circuitry and may be broken by reducing the base potential of transistor 74 sufliciently to cut otf. This reset is accomplished by closing switch 79 which allows diode 120 to lower the base potential of transistor 74 enough to cause the transistor to cut off.

For safety reasons, reset switch 79, when closed discharges capacitor 66 through diode 119 and resistor 80 so that the full prepurge period will be obtained on reset. Also for safety reasons switch '78 is coupled with switch 79 so that switch 78 is always closed grounding the gate of triac 31 when switch 79 is closed.

While transistor 74 is saturated and the system is on lockout, the gate potential of triac 31 is lowered sufliciently by diode 116 and transistor 74 to cause triac 31 to cut off thereby cutting off triac 32 with the consequence that motor 15 slows and stops and switch 16 opens cutting off the DC current supply to line 17.

During lockout transistor 74 is in saturation and capacitor 93 discharges through resistor 92, diode and transistor 74 in preparation for any recycle after reset.

Referring to FIGURE 5, a modified circuit is shown which is identical to the circuit of FIGURE 4 except that the spark detector circuitry is modified to provide for determining whether or not a high resistance short, i.e., 100,000 ohms or less exists between electrodes 13 and 14. The partial short detector comprising components 122 and 123 and elements 121-136 which have been added between the spark detector and the spark pulse integrator to modify the spark detector previously described in connection with FIGURE 2.

The same single burner 10 and associated electrodes -13 and 14 and fuel valve 11 are employed as shown in FIG- URES 1 and 2 as are the same means for bringing line current to motor 15 and spark generator 35-44 and for supplying DC current to line 17.

Spark detector The cathode of diode 45 is connected to the base of transistor 48 and to one plate of capacitor 49, the other plate being connected to line 21 just as in the previously described circuits. Transistor 48 has its emitter connected to line 21 and its collector connected through resistor 50 to line 17 but the collector is also connected to one plate of a capacitor 121 and through a resistor 122 connected to one plate of a capacitor 123 and the base of transistor 51, the other plate of capacitor 123 being connected to line 21. Transistor 51 has its emitter connected to line 21 and its collector connected through resistor 52 to line .17.

The collector of transistor 51 is also connected to the anode of diode 98 but through the cathode-anode, in that order, of'a diode 124. The anode of diode 124 is also connected to the anode of a diode 125 and through a resistor 137 to line 17.

The cathode of diode 125 is connected to the collector of a transistor 126 which collector is also connected through a resistor 127 to line 17. Transistor 126 has its emitter connected to line 21 and its collector also connected through resistor 128 to the base of a transistor 129. The emitter of transistor 129 is connected to line 21 and its collector is connected through a resistor 130 to line -17.

The base of transistor 129 is also connected to the other plate of capacitor 121 and is connected through a resistor 131 to line 21. The collector of transistor 129 is also connected through the anode-cathode of a diode 132 to one plate of a capacitor 133 and through a resistor 134 to line 21.

The other plate of capacitor 133 is connected through a resistor 135 to the base of transistor 126 and is also connected through the cathode-anode of a diode 136 to line 21.

In order to produce a spark discharge between electrodes 13 and 14 the output voltage of the spark discharge voltage generator, i.e., the secondary voltage of transformer 35, must rise rapidly from zero potential to a potential high enough to cause the air gap between the electrodes to ionize, thus causing a spark discharge to occur.

At the time of the spark discharge the voltage between the electrodes Will fall to a much lower potential and oscillate for a period of time, falling to zero as the voltage of transformer falls to zero. During the period of these oscillations, the peak amplitude of the voltage oscillations remains essentially constant for a period of time determined principally by the value of capacitor 38, the effective primary impedance of transformer 35, and the resistance of the air between the electrodes.

In typical working models, with clean electrodes and no leakage paths, the period of constant amplitude oscillations lasts for about 225 microseconds. When a resistance of about 100,000 ohms is connected between electrodes 13 and 14, the period of the oscillations is reduced to about 100 microseconds and a spark discharge does not occur.

Therefore the modified partial short detetor circuit has been arranged so that the train of oscillations must last for more than 175 microseconds in order that the detector circuit will give a positive indication that a spark is occurring.

In operation, components 121, 126-136. comprise a one-shot multivibrator which, in its stable state has transistor 129 saturated and transistor 126 cut off. In the absence of a spark discharge transistor 51 is saturated and capacitor 99 will be at zero charge because charging current is bypassed through diode 124 and transistor 51 and the fuel valve actuating circuit cannot function to open the fuel valve as previously described. Also, in the absence of spark discharges, transistor 48 is cut off and capacitor 121 is charged to about sixty percent of the DC voltage on line 17.

When a spark discharge occurs, transistor 48 saturates but transistor 51 does not ut olf immediately because the charge on capacitor 123 keeps it in saturation until capacitor 123 is almost wholly discharged. However, when transistor 48 saturates, capacitor 121 immediately starts to discharge through transistor 48 and resistor 131 thereby causing a negative voltage .to be applied to the 12 base of transistor 129 and causing this transistor to cut off.

Immediately upon the cut off of transistor 129 the base of transistor 126 starts to draw current through resistor 130, diode 132, capacitor 133, and resistor and transistor 126 saturates. Transistor 129 remains cut off so long as transistor 126 is saturated.

The delay in transistor 51 cutting off, however, is greater than the time taken for transistor 126 to become saturated. The base of transistor 126 continues to draw current until capacitor 133 charges to the point where base current is small enough to cause transistor 126 to cut off again, putting the circuit back intoits stable state, i.e.; transistor 126 out off and transistor 129 saturated.

Component values have been chosen so that the multivibrator remains in the unstable state (transistor-129 cut off and transistor 126 saturated) for about 175 microseconds.

With this arrangement of the spark detector and partial short detector, if a spark discharge is of normal duration of about 225 microseconds, transistor 126 will have changed back to its stable cut off condition after 175 microseconds. Transistor 51 will remain cut off for a further 50 microseconds, i.e., the spark pulse duration of 225 microseconds less the multivibration period of 175 microseconds. Both diodes 124 and 125-are therefore reverse biased for 50 microseconds thereby allowing capacitor 99 to charge through resistor 137 and diode 98, proving the occurrence of a spark discharge and allowing the fuel valve actuating circuit to open the fuel valve.

If the spark discharge signal has a duration of 175 microseconds or less, transistor 51 will have changed back to saturation before, or just as, transistor 126 reverts to its stable cut off condition. This prevents diodes 124 and 125 from both being reversed biased at the same time, with the result that capacitor 99 will not be abe to charge and the fuel valve will remain closed.

' In this embodiment fuel cannot issue at the burner if a spark discharge fails to occur at the electrodes because of shorted or partially shorted electrodes.

Referring to FIGURE 6, a modification of thesystem and circuit shown in FIGURE 5 provides controls for a heating system having two burners, the first burner being a pilot burner 10' and the second burner being the main burner 140. Valve 11 controls the supply of fuel to the first burner and a second solenoid operated fuel valve 141 is provided to control the supply of fuel to the main burner 140.

The sensor device 81 is located adjacent both burners so as to be responsive to each and provision (components 143-147) is made for the actuation of the main burner valve in the sequential operation of the controls. It will be apparent from inspection that the controls for the second burner are adaptable for use also with either the circuit of FIGURE 4 or that of FIGURE 5.

Further provision (components -154) is made in the circuit of FIGURE 6 for a post-purge period. It will be apparent hereinafter that the postpurge control portion of the circuit is adaptable for use in any of the circuits shown in FIGURES 1-5.

Main burner actuator In many burner arrangements it is desirable to first ignite and establish a small burner flame, the pilot burner, so that when the pilot burner is proved to be burning a second, or main, burner fuel valve may be opened, the main burner fuel being ignited by the flame of the pilot burner. Further it is usually desirable to shut off the pilot burner at the end of the proof of ignition period, leaving the control of the main fuel valve dependent on a flame sensor.

The flame sensor circuit of FIGURE 6'is the same as that shown in FIGURES 4 and 5 except'that diode 112 may be omitted as unnecessary as Will appear hereinafter. The gate of an SCR 143 is connected to the collector of transistor 111 of the flame sensor, the anode of SCR 143 being connected through the parallel arrangement of the solenoid armature 144 of valve 141 and a capacitor 145 to a line connected to reference point 22, like the arrangement of SCR 55, capacitor 56 and armature 12 of valve 11. The cathode of SCR 143 is connected to line 21 and a resistor 146 connects its gate also to line 21.

The gate of SCR -5 in the flame sensor amplifier is also connected through the anodecathode in that order of a diode 147 to the cathode of diode 90 in the spark generator control, to the collector of transistor 95 in the proof of ignition timer, and to the base of transistor 117 in the lockout portion of the circuit.

In operation, when pilot burner has been proven to be burning by the flame sensor 81, transistor 111 is in a cut ofi condition and allows the gate of SCR 143 to draw current from line 17 through resistor 114 so that solenoid 1-44 is energized. This opens fuel valve 141 allowing fuel to issue at burner 140 to be ignited by the flame of pilot 10'.

At the end of the proof of ignition period, when transistor 95 saturates, diode 147 which is connected between the gate of SCR 55 and the collector of transistor 95, functions to bypass current to the gate of SCR 55 through transistor 95. SCR '55 then ceases to be conductive and solenoid 12 is no longer energized so that pilot 10' goes out. However, resistor 107 isolates the collector of transistor 111 from this current bypass through diode 147 and SCR 143 continues to draw gate current through resistor 114 so that valve 141 remains open and burner 140 on until the thermostat switch 23 opens.

During the burning period of main burner 140, if the flame is extinguished for any reason, flame sensor 81 detects the absence of flame and the system shuts off and goes on lockout as previously described.

Postpurge control Many types of burners, for safety reasons, require that the com'busion chamber be purged of residual combustion products immediately following the end of a burning period. This is accomplished by allowing the blower motor 15 to run for a period of time after the thermostat switch 23 opens and is referred to as a postpurge period.

In FIGURE 6 the postpurge control portion of the circuit, comprising components 150-154, is inserted between the gate of triac 31 and switch 23 to control triacs 31 and 32. In this modification a transistor 150 has its emitter connected to the gate of triac 31 and its collector connected through resistor to reference point 26.

The base of transistor 150 i-s'connec'ted through a resistor 151 to the junction of the cathode of a diode 152 and one plate of a capacitor 153 and is also adapted to be connected to return line 21 by the closing of reset switch 78 in the reset means. The other plate of capacitor 153 is connected to line 21 and the anode of diode 152 is connected through a resistor 154 and switch 23 in that order to reference point 26.

Diode 152 has its anode also connected to the anode of diode 116 in the lockout portion of the circuit instead of diode 116 being directly connected to the triac 31 gate as in FIGURES 4 and 5.

In operation, when thermostat switch 23 closes calling for heat, capacitor 153 charges through resistor 154 and diode 152. Transistor 150 draws base current from the same source through resistor 151, the emitter being connected through the gate-anode 1 section of triac 31 to line 21. Transistor 150 saturates and allows triac 31 to draw normal gate current from reference point 26 through resistor 30 and the collector-emitter of transistor 150.

Triac 31 is thereby turned on and turns on triac 32 as previously described allowing motor 15 to start and supplying line current to the spark generator. The remainder of the circuit functions as described above in connection with FIGURE 5 and during the heating cycle capacitor 153 remains charged.

When switch 23 opens to end the heating cycle, DC. voltage is removed from line 17 and the fuel valve or valves close. The base current supplied to transistor 150 through switch 23 is cut 011 but the base continues to draw current from capacitor 153 through resistor 151, keeping triacs 31 and 32 conductive so that motor 15 continues to run until the charge on capacitor 153 lessens to the point Where transistor 150 cuts off. This postpurge period is determined primarily by the values of capacitor 153 and resistor 151.

Should the system go on lockout while switch 23 is closed, for any reason, diode 116 and transistor 74 bypass the current from the junction of resistor 154 and diode 152 to the line 21 and diode 152 becomes reversed biased. Transistor 150, therefore, remains saturated only as long as the charge on capacitor 153 can supply base current through resistor 151 to transistor 150, i.e., for the postpurge period.

When the system is shut 01f, either by the opening of switch 23, or by the system going on lockout the combustion chamber will be purged by fresh blower air.

When reset switch 78-79 is closed the base of transistor 150 is grounded and the motor 15 stops running and the system is ready for another cycle after switch 78-79 is opened again.

In construction embodiments of the invention successful control of the burner system was obtained by using the following circuit constants, and these are listed herein merely by way of example and are not intended in any way to limit the invention:

Transformer 20-55, 60 cycle 24 volts, 15 va.

Transformer 35'Spark, small Switch 23-Thermostat switch Switch 16Centrifugal or air switch on motor fan Switches 78 and 79Double pole, single throw, push type DPST.

Triac 31G.E. type SC40B, 200 volt, 6 amp. RMS

Triac 32-R. C.A. type TA2893, 200 volt, 2 amp. RMS

Zener diodes 64 and 69 6.8 volt, /2 watt Zener diode 94-63 volt, /2 Watt Diode 25100 volt, 500 ma., silicon Diodes 4-1 and 42-400 volt, 500 ma. silicon Diodes 45, 68, 72, 90, 98, 112, 115, 116, 119, 120, 124,

125, 132, 136, 147 and 152Ty-pe IN 457 (high conductive silicon diode) Capacitor 27-500 mfd., 25VDC'W, electrolytic Capacitors 66 and 93100 mfd., IOVDCW, electrolytic Capacitor 381 mfd. (for gas) or 2 mid. (for oil) Capacitor 49-.005 mfd., 30 volt Capacitors 121 and 123-.1 mfd., 30 volt Capacitor 133-.01 mfd., 30 volt Capacitor 1535 mfd., 30 volt, electrolytic Capacitor 99'5 mfd., 25 volt, electrolytic Capacitors 56 and 145-200 mfd., 30 volt, electrolytic Capacitor 70100 mfd., 12 volt, electrolytic SCR 55Type C 106Y SCR 58G.E. Type C 106B2 SCR 40200 volt, 3.2 amp., RMS

SCR 14325 volt, 2 amp. DC Transistors 48, 51, 60, 62, 74. 85,

111, 117, 126, 129- and 150 Transistor 73PNP, 2N 3638 Resistors 46 and 65-1 rnegohm, /2 watt Resistor 6322,000 ohm watt Resistors 52, 61, 75, 77, 88, 91, 102,

137 and 154-10,000 ohm, /2 watt Resistor 92-1 rnegohm, watt Resistors 86, 96, 113 and 118-22,000 ohms, watt Resistors and 114-470O ohm, /2 watt Resistors 53, 80, 106, 107, and 146-1000 ohm, /2

watt

87, 95, 101, 104, 109, NPN, 2N3643 15 Resistor 59-500 to 1000 ohm, /2 watt Resistor 44-5000 ohm, 5 watt Resistor 43-100 ohm, 3 watt Resistors 50, 127, 128 and 134-20,000 ohm, /2 watt Resistors 131 and 135 -50,000 ohm, /2 watt Resistor 37-3000 ohm, watt Resistor -500 ohm, 3 watt Resistors 100 and 151-100,000 ohm, /2 watt Resistor 71-l,000,000 ohm, /2 watt While all the transistors, with the exception of transistor 73, are shown and described as NPN transistors, it will be apparent to those skilled in the art that PNP transistors could be substituted by making appropriate changes in the wiring as, for example, by reversal of the voltage detector elements 45 and 46.

What is claimed is:

1. In combination with a fluid fuel burner system having a burner, a solenoid controlled fuel supply valve, an electric blower motor, and a source of electric current having line terminals; an electronic control system comprising: a transformer having its primary winding connected across the line terminals, one line terminal being connected through a first triac to one terminal of the motor and also to one input terminal of a spark discharge voltage generating device, the other line terminal connected by a common return line to the other terminal of the motor and to a second input terminal of the spark discharge device, the spark discharge device having output terminals connected respectively to spark electrodes located adjacent the burner, one electrode being grounded and connected to the common return line, the secondary winding of the transformer having one terminal connected to the common return line and the other terminal connected through the anode and cathode in that order of a diode to one contact of a thermostatically operated switch, the junction of the diode and switch being connected through a first capacitor to the common return line, the other terminal of the switch being connected to a terminal of a second switch and through a resistor to the gate terminal of a second triac, the second switch being normally open and adapted to be closed by the motor reaching its normal operating speed, the other terminal of the second switch being connected to a DC supply line, the gate terminal of the first triac being connected through a resistor and the second triac in that order to the common return line, the solenoid of the fuel supply valve and a second capacitor being connected in parallel between the anode-of the diode and a solenoid switching device that is connected to the common return line, whereby the closing of the first switch initiates sparking at the burner electrodes and turns on the motor which, upon reaching operating speed closes the second switch thereby supplying direct current to the solenoid switching device.

2. In combination with the electronic control system defined in claim 1, a spark detector circuit characterized by said solenoid switching device being an SCR whose anode and cathode are connected in that order between the solenoid and the common return line and having a gateterminal connected to the collector of a first transistor and connected through a resistor to the DC supply line, the first transistor having its emitter connected to the common return line and its base connected through a resistor to the DC supply line, a second transistor having its collector connected to the base of the first transistor and its emitter connected to the common return line, the base of the second transistor being connected through a third capacitor to the common return line, the junction of the common return line and the grounded electrode being connected to the other electrode by a series combination of the anode-cathode of a second diode and a resistor in that order, the cathode of the second diode being connected to the base of the second transistor, whereby the SCR can be turned on only if there is spark discharge voltage at the electrodes.

3. In a device for detecting spark voltage at the elec- 16 trodes of a spark gap, including a source of spark'voltage connected to the electrodes, a circuit comprising: a series connected resistor and diode connected across the electrodes the diode acting as a detector, the junction of the diode and one electrode being connected to ground, and means connected to the output of the diode detector for amplifying the output to a level adequate to operate a switching device for signaling the presence of a spark voltage.

4. The circuit defined in claim 3 characterized by the amplifying means comprising: a source of direct current having a ground terminal, a first transistor, a second transistor, and a capacitor, each transistor having its collector connected through a respective resistor to the source of direct current and its emitter connected to ground, the ouput of the detector being connected through the capacitor to ground, the junction of the output and the capacitor being connected to the base of the first transistor, the base of the second transistor being connected to the collector of the first transistor, and the collector of the second transistor being connected to operate aswitching device for signaling spark voltage at the electrodes.

5. In combination with a fiuid burner system having a burner, a solenoid controlled fuel valve controlling the supply of fuel to the burner, a blower having an electric motor for supplying draft at the burner, and a source of alternating current having line terminals; an electronic control system comprising: a first transformer having its primary winding connected across the line terminals, one line terminal being connected through the anode 1.-anode 2 section of a first triac to one terminal of the blower motor and also to one terminal of spark discharge voltage generating device having input and output terminals and including a second transformen the other line terminal being connected by a common return line to the other terminal of the motor and the other terminal of the spark device, the second transformer having terminals connected respectively to spark electrodes located adjacent the burner, one electrode being grounded and connected to the return line; the secondary winding of the first transformer having one terminal connected to the return line and the other terminal connected through the anode and cathode in that order of a first diodetoa first contact of a thermostatically operated switch, the second contact of the switch being connected through a resistor to the anode of a second diode, thefirst switch contact being connected througha first capacitor to the return line and to the input of a lockout arrangement of transistors for shorting voltage to the return line and having an output, the second switch terminal-being also connected to a direct current supply line through a normally open switch operated by the motor to close when the motor reaches normal operatingspeed, the cathode of the second anode being connected to the return line through a second capacitor and connected through another resistor to the base of a first transistor having its emitter connected to the gate of a second triac, the first transistor collectorbeing connected through another resistor to the first contact of the thermostatically operated switch, the gate of the first triac being connected to the return line through a resistor, the anode l-anode 2 section of the second triac, in that order, the anode of the second diode also being connected to the anode of a third diode whose cathode is connected to the input of the lockout arrangement, and spark detecting means, flame sensing means and timer means connected between the supply line and the return linefor operating the spark generator and fuel valve for controlling said burner whereby the motor is kept running for a short period of time after the fuel valve is closed.

6. The control system as defined in claim-2 together with a second SCR between the spark discharge voltage generating device and the common return line, the second SCR having its cathode connected to the common return line and its gate connected to the collector of a third transistor said latter collector being connected through a resistor to the DC supply line, the third transistor having its emitter connected to the common return line and its base connected to the collector of a fourth transistor and through a resistor to the DC supply line, the fourth transistor having its emitter connected to the common return line and its base connected to the anode of a Zener diode, the cathode of the Zener being connected to the junction of a resistor and one plate of a fourth capacitor, the other plate of the fourth capacitor being connected to the common return line, and the other end of the last named resistor being connected to the direct current line, whereby a prepurge timing period is provided while the motor is running and before the spark generator is turned on.

7. The control system as defined in claim 6 and characterized by having a third diode whose cathode is connected to the collector of the second transistor and whose anode is connected through a resistor to the DC line and connected to the anode of a fourth diode, to the cathode of a second Zener diode, and to one plate of a fifth capacitor; the cathode of the fourth diode being connected to the collector of the third transistor, the other plate of the fifth capacitor being connected to the return line, and the anode of the second Zener being connected to the base of a fifth transistor and to the collector of a PNP transistor; the fifth transistor having its emitter connected to the return line and its collector connected to the base of the PNP transistor, the collector of the fifth transistor also being connected to the gate of the second triac and through a resistor to the first diode, the emitter of the PNP transistor being connected through a resistor to the cathode of the first diode; a first normally open reset switch, adapted to connect the base of the fifth transistor to the return line, and a second normally open reset switch having one contact connected to one plate of the fourth capacitor through a resistor and the other contact connected to the other plate of the fourth capacitor, the two reset switches being linked to close simultaneously.

8. The control system as defined in claim 6 and characterized by having a flame sensor located adjacent the burner, the flame sensor comprising resistance means having a normally high resistance and a comparatively low resistance when there is flame at the burner, the second SCR gate being connected to the third transistor collector through a spark generator control circuit comprising: the collector of the third transistor being connected through a resistor to the anode of a third diode and to the base of a fifth transistor, the fifth transistor having its emitter connected to the common return line and its collector connected to the base of a sixth transistor and, through a resistor to the DC supply line, the sixth transistor having its emitter connected to the return line and its collector connected to the gate of the second SCR and through a resistor to the DC supply line; the collector of the third transistor being also connected to a proof of ignition timer circuit, comprising; a second Zener, a fifth capacitor, and a seventh transistor, the cathode of the second Zener and one plate of the fifth capacitor being connected through a resistor to the third transistor collector, the other plate of the fifth capacitor being connected to the return line and the anode of the second Zener being connected to the base of the seventh transistor, the seventh transistor having its emitter connected to the return line and its collector connected through a resistor to the DC supply line; the collector of the seventh transistor being connected to the cathode of the third diode and being also connected through a resistor to the base of an eighth transistor in a fuel valve actuator circuit, the eighth transistor having its emitter connected to the return line and its collector connected to the DC supply line and to the gate of the first SCR through respective resistors, the base of the eighth transistor being also connected to the collector of a ninth transistor in a spark integrator circuit and through a resistor to the DC supply line, the ninth transistor having its emitter connected to the return line and its base connected through a resistor to one plate of a sixth capacitor and the cathode of a fourth diode, the other plate of the sixth capacitor being connected to the return line and the anode of the fourth diode being connected to the collector of the first transistor; the gate of the first SCR being connected to the collector of the first transistor by a flame sensor amplifier circuit through the spark integrator circuit, the first SCR gate being connected through a resistor to the collector of a tenth transistor which is also connected through a resistor to the DC supply line, the tenth transistor having its emitter connected to the return line and its base connected to the cathode of a sixth diode and the collector an eleventh transistor, the eleventh transistor having its collector also connected through a resistor to the DC supply line, its emitter connected to the return line and its base connected through a resistor to the return line, the latter base also being connected through the flame sensor and a resistor to the DC line; the anode of the sixth diode being connected to the collector of a PNP transistor in a lockout circuit and the anode of a seventh diode in a reset device, the sixth diode anode also being connected to the base of a twelfth transistor, the collector of a thirteenth transistor, and through a resistor to the DC supply line, the thirteenth transistor having its emitter connected to the return line and its base connected to the cathode of the third diode and to the collector of the seventh transistor, the twelfth transistor having its emitter connected to the return line and its collector connected to the base of the PNP transistor, to the cathode of an eighth diode, to the cathode of a ninth diode, and through a resistor to the cathode of the first diode, the emitter of the PNP transistor being also connected through a resistor to the cathode of the first diode, the anode of the eighth diode being connected to the collector of the third transistor, and the anode of the ninth diode being connected to the gate of the second triac; the cathode of the seventh diode in the reset device being connected to one contact of a normally open reset switch, which contact is also connected through a resistor to the cathode of a tenth diode, whose anode is connected to the fourth capacitor and the cathode of the first Zener, the reset switch other contact being connected to the return line and being linked to close simultaneously with a second normally open reset switch adapted on closing to connect the gate of the second triac with the return line.

9. A latching circuit for disabling fuel control circuitry in a fluid fuel burner control system so that the burner is shut off in a safe condition, the fuel control circuitry including a signaling device responsive to an unsafe condition during ignition and operation of the burner, the latching circuit comprising: a pair of complementary transistors each having its base connected to the collector of the other, the collector of one transistor and the emitter of the other transistor being connected through respective resistors to one terminal of a DC source, the emitter of said one transitor being connected to the other terminal of the DC source, the base of said one transistor and the collector of said other transistor being operatively connected to the signaling device, so that when the device responds to an unsafe condition the transistors become saturated, the collector of said one transistor being connected to the fuel control circuity to provide a high conductance path said one transistor when the transistors are saturated, whereby the fuel control circuitry is disabled, said circuitry remaining disabled so long as the latching circuit remains energized.

10. A latching circuit as defined in claim 9 together with manually operable means for rendering the transistors nonconductive.

11. In a device for controlling the operation of a fluid fuel burner, a timing circuit having a positive voltage output signal for a fixed period when first energized and thereafter having a signal substantially of zero voltage, comprising: a source of direct current having a ground terminal, a Zener diode, a transistor, resistance means, and a capacitor, the transistor having its emitter connected to ground and its collector connected through a resistor to the source of direct current and connected to an output terminal, the base of the transistor being connected to the anode of the Zener diode, the cathode of the Zener diode being connected through the capacitor to ground and connected through a resistor to the source of direct current, whereby the output terminal is at a positive potential until the transistor conducts after said fixed period.

12. The control system as defined in claim 8 characterized by having the collector of said second transistor connected to the base of the first transistor through a resistor and being also connected to a seventh capacitor, the base of the first transistor also being connected to one plate of an eighth capacitor whose other plate is connected to the return line, the collector of the first transistor being connected to the fourth diode through the cathode and anode in that order of an eleventh diode, the anode of the fourth diode also being connected through a resistor to the supply line and through the anode and cathode in that order of a twelfth diode to the collector of a fourteenth transistor whose emitter is connected to the return line, the collector of the fourteenth transistor being also connected through a resistor to the DC supply line and con-nected through a resistor to the base of a fifteenth transistor and to the other plate of the seventh capacitor which plate is also connected through a resistor to the return line, the fifteenth transistor having its emitter connected to the return line and its collector connected to the anode of a thirteenth diode and through a resistor to the DC supply line, the cathode of the thirteenth diode being connected to one plate of a ninth capacitor and through a resistor to the return line, the other plate of the ninth capacitor being connected to the cathode of a fourteenth diode and through a resistor to the base of the fourteenth transistor, the anode of the fourteenth diode being connected to the return line, whereby a one-shot multivibrator is formed in the spark detector portion of the circuit for rendering detector inoperative for a fixed period of time after the initiation of each spark discharge.

13. The circuit defined in claim 3 characterized by the means for amplifying the output of the diode detector including means for rendering the output unamplified for a predetermined period so that the signal is amplified only if the spark discharge at the electrodes is of a duration in excess of said period and comprising: a source of direct current having a ground terminal; a first transistor, a second transistor, and a capacitor, each transistor having its collector connected through a respective resistor to the source of the direct current and its emitter connected to ground, the output of the detector being connected through the capacitor to ground, the junction of the output and the capacitor being connected to the base of the first transistor, the base of the second transistor being connected through a resistor to the collector of the first transistor and being connected through a second capacitor to ground; the collector of the first transistor being connected through a third capacitor to the base of a third transistor, the collector of the second transistor being connected through the anode-cathode in that order of a second diode to an output terminal connected to operate a switching device for signaling spark voltage at the electrodes, the base of the third transistor being connected through a resistor to ground and being connected through a resistor to the collector of a fourth transistor and to the cathode of a third diode whose anode is connected to said output terminal, the third and fourth transistors having their collectors connected through respective resistors to the source of direct current and their emitters connected to ground, the base of the fourth transistor being connected through a resistor to one plate of a fourth capacitor and to the cathode of a fourth diode whose anode is connected to ground, the other plate of the fourth capacitor being connected through a resistor to ground and being connected through the cathode-anode in that order of a fifth diode to the collector of the third transistor, whereby the output of the detector is amplified only when the fourth transistor is not conducting.

14. The control system as defined in claim 12 characterized by having a second burner adjacent the flame sensor and a second solenoid-controlled valve for supplying fuel to the second burner, the solenoid of the second fuel valve being connected in parallel with a tenth capacitor between the direct current supply line and the anode of a third SCR, the cathode of the third SCR being connected to the return line and the gate of the third SCR being connected through a resistor to the return line and also being connected to the collector of the tenth transistor, the gate of the first SCR being also connected through the anode and cathode in that order of a fifteenth diode to the junction of the collector of the seventh transistor, the cathode of the third diode, and the base of the thirteenth transistor, whereby the second fuel valve is turned on after the first burner is lit and turns off when the first switch opens and when the flame sensor fails to detect a flame at either burner.

15. In a device for controlling the operation of a fiuid fuel burner having a source of alternating current, a source of direct current with one terminal grounded, an electric motor and a direct-current-operated switching device connected in series across the source of alternating current, and means including a thermostat switch for controlling the supply of fuel to the burner; a timer circuit, comprising: a series combination of a resistor, the anode-cathode in that order of a diode, and a capacitor connected to ground connecting the source of direct current through the thermostat switch to ground; the junction of the diode and capacitor being connected through a resistor to the base of a transistor, the collector of the transistor being connected through a resistor to the source of direct current and the emitter of the transistor being connected to ground through the direct-current-operated switching device; whereby the motor continues to run for a predetermined period after the thermostat switch opens.

16. In a device for controlling the operation of a fluid fuel burner having a source of alternating current, a source of direct current, an electric motor for supplying draft to the burner, a first triac having its anode l-anode 2 section connected in series with the motor across the source of alternating current, a series combination of a resistor and the anode l-anode 2 section of a second triac in that order connecting the gate of the first triac across the source of alternating current, and switch means connected across the source of alternating current for operating a fuel valve controlling the supply of fuel to the burner; a timer circuit comprising: a thermostatically operated switch, a diode, a capacitor, resistance means, and a transistor; the emitter of the transistor being connected to the gate of the second triac and the collector-emitter circuit of the transistor connecting the gate circuit of the second triac through a resistor across the source of direct current; the thermostatically operated switch, a second resistor, the anode-cathode of the diode, and the capacitor being connected in series in that order across the source of direct current; the junction of the second resistor and the diode being operably connected to the fuel valve switch means; the junction of the diode and the capacitor being connected by a resistor to the base of the transistor, whereby the motor remains running for a period after the fuel valve is turned off and the thermostatically operated switch is open.

17. A gas ignition and burner control system comprising in combination, a source of alternating current, a burner having a motor and blower driven thereby, an

electrical valve controlled source of fuel, spark gap electrodes disposed adjacent the burner for ignition of fuel issuing from the burner, a thermostatic switch, a combined ignition and control circuit and a switch responsive to blower operation, said combined ignition and control circuit having means for deriving direct current control voltage from said alternating current source and connections through said thermostatic switch, a spark generator for said gap electrodes, and means for closing a circuit to said motor and spark generator from said alternating current source upon closing of said thermostatic switch, said last named circuit comprising connections for said direct current voltage means through said blower responsive switch for energizing said electrical valve controlled source of fuel, said last named connections including a spark detector for preventing energizing of said valve controlled source of fuel upon failure of said detector to prove the regular occurrence of spark voltage.

18. A circuit in accordance with claim 17 wherein the combined circuit includes a capacitive charging timer and switch means actuated thereby after a predetermined time and in which said switch means is interposed in circuit with said spark generator to delay the occurrence of spark generation, whereby to provide a burner purge period before attempting ignition and fuel supply.

19. A circuit in accordance with claim 17 wherein the combined circuit includes a timer means whose operation is initiated by said spark detector on failure of said detector to prove the regular occurrence of spark voltage, and a latching type disabling circuit actuated by said timer means after a predetermined period, and adapted for opening said circuit closing means to cut off said motor and spark generator from the alternating current source.

20. A gas ignition and burner control system comprising in combination, a source of alternatingcurrent, a burner, an electrical valve controlled source of fuel, spark gap electrodes disposed adjacent the burner for ignition of fuel issuing from the burner, a thermostatic switch, a combined ignition and control circuit having means for deriving direct current control voltage from said alternating current source and connections through said thermostatic switch, a spark generator for said gap electrodes, and means for closing a circuit to said spark generator from said alternating current source upon closing of said thermostatic switch, said last named circuit comprising connections for said direct current voltage means for energizing said electrical valve controlled source of fuel, said last named connections including a series resistor diode spark gap voltage detector for preventing energizing of said valve controlled source of fuel upon failure of said detector to prove the regular occurrence of spark voltage.

21. A gas ignition and burner control system comprising in combination, a source of alternating current, a burner having a motor and blower driven thereby, an electrical valve controlled source of fuel, spark gap electrodes disposed adjacent the burner for ignition of fuel from the burner, a thermostatic switch, a combined ignition and control circuit and a switch responsive to blower operation and a flame sensor, said combined circuit having means for deriving direct current control voltage from said alternating current source and connections through said thermostatic switch, a sprak generator for said gap electrodes, and means for closing a first circuit to said motor and partially to said spark generator from said alternating current source upon closing of said thermostatic switch, said first circuit comprising connections for said direct current voltage means through said blower responsive switch to a time delay circuit completing the application of said alternating current source to said spark generator after a predetermined period of time, and for energizing said electrical valve controlled source of fuel, operation of said delay circuit commencing on application of direct current voltage to said delay circuit and finishing after said predetermined period of time, said last named connections including a series resistor diode spark gap voltage detector for preventing energizing of said valve controlled source of fuel until said detector proves the regular occurrence of spark voltage, and means for said flame sensor to de-energize said valve in response to said flame sensor indicating the absence of flame, and a second time delay circuit acting on said last named means to prevent the de-energization of said valve by said flame sensor for a predetermined period of time after the opening of said valve.

22. A circuit in accordance with claim 21 wherein the combined circuit includes a timer means including circuit means for maintaining closed said first circuit for a predetermined period after said valve is deenergized.

23. A gas ignition and burner control system comprising in combination, a source of alternating current, a burner, an electrical valve controlled source of fuel, spark gap electrodes disposed adjacent the burner for ignition of fuel from the burner, a flame sensor adjacent the burner to indicate the presence or absence of flame at the burner, a thermostatic switch, a combined ignition and control circuit having means for deriving direct current control voltage from said alternating current source and connections through said thermostatic switch, a spark generator for said gap electrodes and means for closing a circuit to said spark generator from said alternating current source upon closing of said thermostatic switch, said last named circuit comprising connections for said direct current voltage means for energizing said electrical valve controlled source of fuel and including a series resistor diode spark gap voltage detector for preventing energization of said electrical valve until said detector proves the regular occurrence of spark voltage, and means for said flame sensor to de-energize said electrical valve in response to absence of flame at said burner, and time delay means acting on said last named means for delaying response thereof for a predetermined interval after the energizing of said electrical valve.

24. A gas ignition and burner control system comprising in combination, a source of alternating current, a burner having a motor and blower driven thereby, an electrical valve controlled source of fuel, spark gap electrodes disposed adjacent the burner for ignition of fuel from the burner, a flame sensor adjacent the burner for indicating the presence or absence of flame at the burner, a thermostatic switch, a combined ignition and control circuit and a switch responsive to blower operation, said combined circuit having means for deriving direct current control voltage from said alternating current source and connections through said thermostatic switch, a spark generator for said gap electrodes and means for closing a first circuit to said motor and partially to said spark generator from said alternating current source upon closing of said thermostatic switch, said first circuit comprising connections for said direct current voltage means through said blower responsive switch to a first time delay circuit for completing the application of said alternating current source to said spark generator after a predetermined period of time, said predetermined period of time commencing on application of said direct current control voltage to said first time delay circuit, said time delay circuit also applying said direct current voltage to a valve energizing circuit for deenergizing and closing said valve in response to said flame sensor indicating the absence of flame at said burner and a second time delay circuit for delaying the response of said valve circuit to said flame sensor for a predetermined period of time after said direct current voltage is applied to said valve circuit, whereby to provide a trial for ignition period and a series resistor diode spark gap voltage detector operative on said valve energizing circuit to open said valve during said trial for ignition period.

25. A gas ignition and burner control system comprising in combination a source of alternating current, a pilot burner, a main burner, a motor and blower driven there by, spark gap electrodes disposed adjacent said pilot burner for ignition of gas issuing therefrom, a flame sensor 23 adjacent both said pilot and main burners to detect presence or absence of flame at either of said burners, a thermostatic switch, an electrically operated pilot fuel valve, an electrically .operated main fuel valve, 3. combined ignition and control circuit and a switch responsive to blower operation having means for deriving direct current control voltage from said alternating current source, a spark generator for said gap electrodes operative in response to a direct current voltage, a first circuit including first time delay means to supply said alternating current source to said motor and said spark ge'nerator upon closing of said thermostatic switch, said first circuit including connections for said direct current voltage means through said thermostatic switch and said blower responsive switch for energizing further control circuitry comprising a pilot valve circuit for opening said pilot valve in response to a direct current voltage, a main valve circuit for opening said main valve, a second time delay means, a third time delay means, a disabling circuit for rendering said combined circuit inoperative including a manually operated reset circuit, a series resistor diode spark gap voltage detector having a direct current voltage output indicating occurrence of sparks, said second time delay means having connections to said spark generator and to said third time delay means to apply direct current voltage thereto after a predetermined period in response to the closing of said thermostatic switch and said blower responsive switch, said spark detector including connections to said pilot valve circuit for opening said pilot valve in response to said spar-k detector indicating the occurrence of sparks, said third time delay means having connections to said spark generator and to said pilot valve circuit thereby to render said generator and said pilot valve circuit inoperative after a predetermined period of time and having a further connection to said disabling circuit to cause the operation thereof after said predetermined period of time in the event that said flame sensor is indicating the absence of flame at said main burner, said main valve circuit opening said main valve in response to said flame sensor indicating the presence of flame at said pilot burner and maintaining said main valve open after said pilot valve has been closed so long as said flame sensorrcontinues to indicate the presence of flame at said main burner, said disabling circuit having connections to said cfirst time delay means whereby said first time delay means will cause said first circuit to break the supply of said alternating current to said motor after a predetermined interval in response to the operation of said disabling circuit, said disabling circuit having a supply from said direct current voltage means independent of said thermostatic switch and said blower responsive switch whereby the disabling operation is discontinued by the momentary closing by manual means of a switch in said reset circuit, said first time delay means also in response to the opening of said thermostatic switch causing said first circuit to break the supply of alternating current to said motor after a predetermined interval.

References Cited UNITED STATES PATENTS 1,755,390 4/ 1930 Fischer et a1. 2,628,676 2/1953 Shottenfeld 158-128 2,839,129 6/1958 St. Clair. 2,964,102 12/1960 Cassell et a1 158-125 X 3,115,180 12/1963 Deubel 158-124 3,126,940 3/ 1964 Lundberg. 3,277,949 10/1966 Walbridge 158-125 3,291,183 12/1966 Fairley 158-125 X 3,306,339 2/1967 Barton et a1 158-124 FREDERICK KETTERER, Primary Examiner.

U.S. Cl. X-R. 

